Okay, not sure if my presence will be of any use (a 16 year old is seldom helpful in this kind of situation), but I'd be interested to know about what the teachers knew at the time of the incidents and their take on it all. From what you're saying, it looks as if they already knew, and it's almost as if they WANT 'R' expelled. Considering that if that's what they want (if it turns out to be true), then they're just idiots and it'll probably be best to pull him out yourself. Other than that, fight for 'R's position for all it's worth.
If 'R' does get let back, make SURE that EVERY teacher knows about the rules that 'R' requires, and that they can actually tell when 'R' goes into shutdown, if possible. When you do so, keep ALL evidence, such as e-mails, letters, and even the notices given out by the school if possible (they could've been vague on the situation) and include with them dates and such, so that if this happens again (and judging from what's going on over there, it's a likely possibility), you can sue their asses for it. Be as careful and pay as much attention to detail as you can, almost like a criminal.
Because of 'R's high marks, it shows he obviously does care about school-work and is not a bad person, and if the school, or at least those who run it, can't see that, you may as well put him into another school or do home-teaching.
_________________
I was sad when I found that she left
But then I found
That I could speak to her,
In a way
And sadness turned to comfort
We all go there